Most patients with diabetes mellitus who receive insulin therapy develop anti-insulin antibodies. In some cases, the immune response to insulin may dramatically compromise therapy because of allergic reactions or resistance to insulin. In addition, anti-insulin antibodies may aggravate vascular complications such as retinopathy and nephropathy. The fine specificity of the immune response to mammalian insulins has been well characterized in inbred animals, and these responses are under the control of MHC-linked immune response genes. In contrast, there are virtually no data on the cellular and regulatory components of the immune response to insulin man. In order to understand the cellular and genetic mechanisms that regulate the human immune response to insulin, we have designed studies to dissect the determinants on the insulin molecule which are antigenic in man. These studies of specificity will be carried out in assays of both cellular and antibody activity. We have developed an antigen-specific, accessory cell dependent assay of T lymphocyte proliferation in insulin immune individuals. Using this assay, we have begun to localize determinants recognized by lymphocytes responsive to animal insulins, human biosynthetic insulin, and A and B peptides. Experiments are designed to examine the role of human Ia-like antigens (HLA-DR) in the in vitro response. Studies of families with several diabetics will examine associations between DR type(s) and responsiveness to determinants on the insulin molecule. Our studies of the humoral response employ native insulins, derivatized insulins, and peptides to identify the predominant sites recognized by anti-insulin antibodies. In addition, we have begun to analyze the isotypes and isoelectric focusing spectrotypes of anti-insulin antibodies. This information will be used in future studies on the structural diversity of insulin antibodies. Our studies will broaden therapeutic capabilities by identifying residues which may be modified in order to alter the immunogenicity of insulin preparations. The immunogenic potential of human insulin will be determined in individuals sensitized to heterologous insulin and in new diabetics treated with human insulin. This study will provide insight into the role of insulin immunity in the pathogenesis and in complications of diabetes mellitus. In addition, this defined antigen is a unique tool for investigation of the complexities of the human immune response.